Given a string s, partition s such that every substring of the partition is a palindrome.

Return the minimum cuts needed for a palindrome partitioning of s.

For example, given s = "aab",
Return 1 since the palindrome partitioning ["aa","b"] could be produced using 1 cut.

定义状态 f(i,j) 表示区间 [i,j] 之间最小的 cut 数，则状态转移方程为
f(i, j) = min { f(i, k) + f(k + 1, j) } , i  <=k <= j, 0 < i <=  j <= n

我们求解的是整个字符串的最小cut数，可以从字符串的头开始，也可以从尾部开始